Mineral Trioxide Aggregate (MTA)-like Materials: An Update Review

September 2014Issue - Expires September 30th, 2017

Compendium of Continuing Education in Dentistry

Abstract

Mineral trioxide aggregate (MTA) is a multi-application material used in endodontics. It is a mixture of a refined Portland cement and bismuth oxide and trace amounts of SiO2, CaO, MgO, K2SO4, and Na2SO4. MTA powder is mixed with supplied sterile water in a 3:1 powder/liquid. Hydrated MTA has an initial pH of 10.2, which rises to 12.5 three hours after mixing. There are several materials derived from MTA such as Endo-CPM Sealer, Ortho MTA, MTA-Fillapex, DiaRoot BioAggregate, MTA Bio, light-cured MTA, tricalcium silicate, and iRoot SP. The purpose of this article is to review MTA-like materials.

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Undoubtedly, one of the most important goals of dentistry is to preserve natural dentition. In order to do so, several materials have been introduced, including mineral trioxide aggregate (MTA). MTA is a biomaterial that has been extensively investigated for endodontic applications since the early 1990s. It was first described in 1993, and a patent was taken out for it in 1995.1

Constituents of MTA

MTA is a mixture of a refined Portland cement and bismuth oxide and trace amounts of silicon dioxide (SiO2), calcium oxide (CaO), magnesium oxide (MgO), potassium sulfate (K2SO4), and sodium sulfate (Na2SO4).2 Portland cement is a mixture of dicalcium silicate, tricalcium silicate, tricalcium aluminate, gypsum, and tetracalcium aluminoferrite.2 Gypsum and, to a lesser extent, tetracalcium aluminoferrate are important determinants of setting time.2 MTA may contain approximately half the gypsum content of Portland cement, as well as smaller amounts of aluminum species, which provides a longer working time than Portland cement. MTA has smaller mean particle size, contains fewer toxic heavy metals, has a longer working time, and has undergone additional processing/purification than regular Portland cements.1

The MTA powder is mixed with supplied sterile water in a 3:1 powder/liquid ratio, and it is recommended that a moist cotton pellet be temporarily placed in direct contact with the material and left until a follow-up appointment.3 Upon hydration, MTA materials form a colloidal gel that solidifies to a hard structure in approximately 3 to 4 hours, with moisture from the surrounding tissues purportedly assisting the setting reaction.3 Hydrated MTA has an initial pH of 10.2, which rises to 12.5 three hours after mixing.4 The setting process is described as a hydration reaction of tricalcium silicate (3CaO·SiO2) and dicalcium silicate (2CaO·SiO2); the latter is said to be responsible for the development of material strength. The compressive strength of MTA increases in the presence of moisture for up to 21 days, while MTA microhardness and hydration behavior has been reported to be adversely affected with exposure to the pH range of inflammatory environments (pH = 5) as compared to physiologic conditions (pH = 7).1

White-Colored MTA

Prior to 2002, only one MTA material consisting of gray-colored powder was available. That year white MTA (WMTA) was introduced to address esthetic concerns. Using scanning electron microscopy (SEM) and electron probe microanalysis, it was found that the major difference between gray MTA (GMTA) and WMTA is in the concentrations of aluminum oxide (Al2O3), MgO, and iron(II) oxide (FeO). WMTA was found to have 54.9% less Al2O3, 56.5% less MgO, and 90.8% less FeO, which leads to the conclusion that the FeO reduction is most likely the cause for the color change. WMTA was also reported to possess an overall smaller particle size than GMTA, while it was additionally suggested the reduction in magnesium could also contribute to the lighter color of WMTA.1,5

MTA-like Materials

Acroseal

Acroseal (Septodont) is a biocompatible calcium hydroxide-based sealer composed of a base and a catalyst. The base contains methylene amine (hexamethylenetetramine) and glycyrrhetinic acid (enoxolone), and the catalyst contains calcium hydroxide and bisphenol A diglycidyl ether (DGEBA) resin. Both pastes contain a radiopaque excipient. Enoxolone (C30H46O4) has antibacterial properties.

A new formulation of MTA-labeled Endo-CPM Sealer (EGEO S.R.L.) was created to be used as root canal sealer. According to the manufacturer,7 the composition of CPM Sealer after mixing is: MTA (SiO2, potassium oxide [K2O], Al2O3, sulfur trioxide [SO3], CaO, and bismuth[III] oxide [Bi2O3]), 50%; SiO2, 7%; calcium carbonate (CaCO3), 10%; Bi2O3, 10%; barium sulfate (BaSO4), 10%; propylene glycol alginate, 1%; propylene glycol, 1%; sodium citrate, 1%; and calcium chloride, 10%. The chemical composition of CPM sealer is similar to that of MTA, but with the addition of calcium carbonate to reduce the pH from 12.5 to 10 after set. This way, the surface necrosis in contact with the material is restricted, which allows the action of the alkaline phosphatase.8-10

Recently, Mohammadi et al11 showed that the antibacterial activity of Endo-CPM Sealer and WMTA against staphylococcus aureous was not significantly different from each other in 24-hour as well as 7-day samples, but CPM sealer demonstrated significantly greater effect against streptococcus mutans than WMTA. Gomes-Filho et al8 evaluated the rat subcutaneous tissue response to implanted polyethylene tubes filled with Endo-CPM Sealer (Portland Cement Modified Sealer) (EGEO S.R.L.) compared with Sealapex (SybronEndo) and Angelus MTA (Angelus). According to their results, both materials caused mild to moderate reactions at 7 days that decreased with time. The response was similar to the control on the 30th day with Endo-CPM Sealer and Angelus MTA and on the 60th day with Sealapex. Mineralization and granulations birefringent to the polarized light were observed with all materials.

Ortho MTA

OrthoMTA (BioMTA) was recently introduced in the Republic of Korea with the aim of decreasing heavy metal contents of root repair materials. Featuring a fine granularity of only 2 microns, Ortho MTA penetrates into dental tubules and fuses itself to the surface where it is applied. In addition, it prevents microleakage by forming an interfacing layer of hydroxyapatite (HA) between the Ortho MTA and the canal wall. Furthermore, it exhibits a bioactive characteristic in that it releases calcium ions through the apical foramen and neutralizes the apical portion of the root, thus forming an interfacial HA layer and releasing calcium ions, which induce regeneration of the apical periodontium. Components of Ortho MTA include dicalcium silicate, tricalcium silicate, tricalcium aluminate, tetracalcium aluminoferrite, free calcium oxide, and bismuth oxide.12

MTA-Fillapex

MTA-Fillapex (Angelus) is an MTA-based root canal sealer. It is available in two packages: MTA-Fillapex 12g + mixing pad + 20 automix tips, and MTA-Fillapex refill 4g + five automix tips. The working and setting times of MTA-Fillapex are 30 minutes and 120 minutes, respectively.13

BioAggregate handles well after mixing with water, which aids in the repair process of the affected tooth. The material’s radiopacity properties, convenient setting and hardening time, and easy workability and handling properties make it well suited for root canal filling. Six 1-gram BioAggregate packages come in each box with eight vials of BioA liquid with six mixing trays and spatulas.

When iRoot series BioAggregate powder is hydrated, the BioA Liquid precipates calcium phosphate, which is what comprises human bone. During this reaction, hydroxyapatite is created and water is formed. The water supplied through this dynamic reaction contributes to the hydration reaction speed, as well as the the setting time and strength of BioAggregate.15,16

BioAggregate also is available as DiaRoot Root Canal Repair Filling Material, which is a private label distributed by DiaDent Group International.

MTA Bio

MTA Bio (Angelus) is a cement that is fully synthesized in a laboratory under controlled, clean, and segregated conditions to ensure a contaminant-free final product. The goal is to produce a product with the pro-analysis designation, guaranteeing the highest analytical quality. As a result of the high-quality control of the cement production, the final cement is free of undesirable contaminant substances, in particular, arsenic. Furthermore, it has been stated that the handling properties, as well as the setting time, were improved.17,18 Vivan et al19 evaluated the pH, calcium release, setting time, and solubility of two commercially available MTA cements (white MTA Angelus and MTA Bio), light-cured MTA and a resin-based cement. According to their results, the white MTA Angelus and MTA Bio had the shortest setting times, higher pH and calcium ion release, and the highest solubility. In contrast, the epoxy resin-based cement and light-cured MTA showed lower values of solubility, pH, and calcium ion release. In another study, Lessa et al17 assessed the cytotoxicity of white MTA and MTA Bio on odontoblast-like cell culture and found that both materials presented low cytotoxic effects. Borges et al20 evaluated the radiopacity of gray and white structural and nonstructural Portland cement, gray and white ProRoot® MTA (DENTSPLY Tulsa Dental Specialties) and MTA Bio. Findings indicated that the radiopacity of MTA Bio was somewhat lower than white ProRoot MTA and gray ProRoot MTA.

Light-Cured MTA

An experimental light-cure MTA has been developed to have similar properties to MTA, but with better working properties. This material can be packed in small plastic tubes with disposable aluminum tips that facilitate its insertion. Resinous formulation can enable light-cure and immediate setting. The material’s formulation consists of hydrophilic resins that are reportedly biocompatible and the active ingredients of Portland cement. The light-cure formulation has been demonstrated in laboratory studies, retaining its alkaline pH for a period of a year. This alkaline environment should encourage the development of its biologic properties.21,22

Tricalcium Silicate

Tricalcium silicate, the main component of MTA, has been used on its own or with additives as bone cement, as a die material for the plastic-forming process by extrusion when admixed with cellulose-based polymers, and as a posterior restorative material and a root filling material in dentistry.23 Tricalcium silicate has exhibited adequate physical properties24 and has induced cell growth and differentiation and also the deposition of hydroxyapatite on its surface.25 Tricalcium silicate can be manufactured by the sol-gel method using pure raw materials unlike the raw materials used in the manufacture of Portland cement. The sol-gels are transformed into ceramics by heating at relatively low temperatures. Tricalcium silicate has been postulated to be able to replace the cement component in MTA due to similar composition and bioactivity of the material.26

Portland cement has a 68% composition of tricalcium silicate. On hydration, both Portland cement and tricalcium silicate reacted with water to form calcium silicate hydrate and calcium hydroxide. This reaction is typical of calcium silicates and has been reported both for industrial Portland cements23 and for MTA,27,28 which is composed of 80% Portland cement. Both hydrated cements were composed of unreacted cement particle surrounded by a rim of hydration product. This rim of hydration product was mostly calcium silicate hydrate interspersed with some calcium hydroxide. Both cements produced calcium hydroxide, with the tricalcium silicate producing more calcium silicate hydrate and calcium hydroxide. Both cements were completely hydrated by 28 days of curing with low amounts of tricalcium silicate present in the hydrated cement.23

Biomimetic Carbonated Apatite

Carbonated apatite is known as biologic apatite and represents the mineral phase of hard tissue; therefore, it is more similar to bone apatite than pure HA.29,30 This nonstoichiometric apatite is soluble in acid condition because of its low crystallinity.30 Bozeman et al31 postulated that an optimum amount of this precipitate (HA) might be required to initiate osteogenic activity. It has been shown that sintered carbonated apatite possesses osteoconductive and bioresorption properties.30

iRoot® SP

iRoot® SP (Innovative BioCeramix, Inc.) is composed of zirconium oxide, calcium silicate, calcium phosphate, calcium hydroxide, filler, and thickening agents, with a setting time of 4 hours. iRoot SP is a convenient, premixed, ready-to-use injectable white hydraulic cement paste developed for permanent root canal filling and sealing application. It forms excellent bonding with root canal dentin, penetrating into the dentin structure, and it can directly be used for filling root canals with or without gutta-percha points.32,33 The material is insoluble and radiopaque, and, furthermore, iRoot SP has non-shrinkage characteristics during setting and excellent physical and chemical properties. Due to its bioceramic composition, iRoot SP is biocompatible and non-toxic. Additionally, it has excellent sealing and handling abilities. It is available in a pre-loaded single syringe with disposable intracanal tips.32-34

The addition of sodium fluoride (NaF) 1% wt to calcium silicate powder causes a delay in the setting time and increases expansion36 and long-term apical sealing ability in the root canal.37 Furthermore, an increase in NaF content (from 0% to 10% wt) results in an enhanced solubility of F-doped MTA cements in water or in Dulbecco’s modified eagle medium (DMEM).38

EndoBinder

EndoBinder (Binderware) is a new calcium aluminate-based cement. The purpose of the introduction of EndoBinder was to preserve the properties and clinical applications of MTA without its negative characteristics. EndoBinder is composed of (% by weight) Al2O3 (≥ 68.5%), CaO (≤ 31%), SiO2 (0.3% to 0.8%), MgO (0.4% to 0.5%), iron(III) oxide (Fe2O3) (< 0.3), which presents adequate biological and antimicrobial properties. The cement is produced by the process of calcining Al2O3 and CaCO3 at temperatures between 1315°C and 1425°C, the most feasible method for the production of materials with a more uniform composition. The calcium aluminate formed is cooled and then triturated until the adequate particle size is obtained.39,40

The formation of EndoBinder can be described by the following chemical reaction: CaCO3 + Al2O3 = Ca(AlO2)2 + CO2.

EndoBinder has been developed for several reasons. First, because it is destined for dental applications, the selection of the reagent materials allows control of the level of impurities such as Fe2O3, which promotes tooth darkening, and free MgO and CaO, which might be responsible for an undesirable level of expansion of the material in contact with humidity. Second, although calcium hydroxide and MTA contribute to making the environment inhospitable to the growth of bacteria, an excessive concentration after its hydration might contribute to fibrosis of the adjacent tissues. Thereafter, the balance between the phases rich in Al2O3 and CaCO3 allowed by EndoBinder promotes better results with regard to biocompatibility and the physicochemical properties of the cement. The third reason is the formation of autogenous phases capable of helping to control the setting time of cement, thereby avoiding the inclusion of unnecessary additives.41,42

Calcium-enriched mixture (CEM) cement was introduced to dentistry as an endodontic filling material. The major components of the cement powder are calcium oxide (CaO), sulfur trioxide (SO3), phosphorous pentoxide (P2O5), and silicon dioxide (SiO2), different from MTA and Portland cement. The physical properties of this biomaterial, such as flow, film thickness, and primary setting time, are favorable.44

The sealing ability of CEM is similar to MTA45 and improves through storage in phosphate-buffered saline solution.46 The particle size of CEM is smaller than MTA47; this may be related to its acceptable sealing properties. It has the ability to promote hydroxyapatite formation in saline solution48 and might promote the process of differentiation in stem cells and induce hard-tissue formation, that is, cementogenesis. Antibacterial properties of CEM, calcium hydroxide (CH), MTA, and Portland cement have been compared in a number of studies; the results have shown that CEM has antibacterial properties similar to CH.44 Comparison of antifungal properties of CEM and MTA on Candida albicans has shown that both biomaterials induce complete death of fungal cells after 24 hours.49 According to Asgary et al,50 CEM has an alkaline pH of ~11, which is important in the antimicrobial properties of this biomaterial. Asgary et al51 as well as Tabarsi et al52 demonstrated that in various forms of vital pulp therapy, the induction of dentin bridge formation in CEM was comparable with that in MTA and superior to that in CH. Studies of complete pulpotomy treatment using CEM, MTA, and CH have shown that compared to CH, samples in the CEM group exhibited lower inflammation, improved quality/thickness of calcified bridge, superior pulp vitality status, and morphology of odontoblast cells. However, no significant differences were identified in comparison to MTA.44 Studies using the MTT assay on L929 as well as scanning electron microscope (SEM) on human gingival fibroblast (HGF) indicated that the cytotoxic potentials of CEM and MTA were similar and both biomaterials were significantly superior to IRM.53-55 A recent study comparing the subcutaneous tissue response to CEM and MTA in rats showed that unlike MTA, CEM did not induce any cellular necrosis after 1 week. After 60 days, levels of inflammation in the CEM group were significantly lower than the white/gray MTA groups. Another significant finding was the presence of dystrophic calcification adjacent to the biomaterials, which is an indication of their osteo-inductive potential.56

Conclusion

Mineral trioxide aggregate (MTA) is a multi-application material for use in endodontics, offering favorable properties such as biocompatibility, good sealing ability, and the ability to promote dental pulp and periradicular tissue regeneration. This article has reviewed a variety of MTA-like materials that have been introduced for endodontic applications.

DISCLOSURE

The authors have no affiliation with any of the companies mentioned in this article.